1. Field of the Invention
The present invention relates to vapor compression refrigeration systems which are adapted to chill a fluid for domestic or other uses. More particularly the present invention relates to vapor compression refrigeration systems which utilize a flash economizer to cool liquid refrigerant.
2. Description of the Prior Art
Refrigeration systems of vapor compression type typically employ a compressor to increase the temperature and pressure of the gaseous refrigerant. Connected thereto is a condenser wherein gaseous refrigerant is cooled so that it may change state to a liquid refrigerant. Thereafter the liquid refrigerant may be cooled in a flash economizer wherein part of the refrigerant is vaporized absorbing heat from the remaining liquid refrigerant. Vaporized refrigerant has been typically drawn into the compressor for recycling through the condenser and liquid refrigerant which has now been cooled passes on to the evaporator or chiller. In the chiller, the refrigerant is evaporated absorbing heat from the fluid to be cooled, the now gaseous refrigerant being drawn into the compressor to complete the cycle.
In the above described refrigeration system, the compressor is a multi-stage compressor such that the flashed refrigerant from the flash economizer may be drawn into the compressor between the stages allowing the flash economizer to be at an intermediate pressure to the condenser and the chiller. The basic patent dealing with the flash economizer was issued to Jones in 1942 and is entitled "Refrigeration", U.S. Pat. No. 2,277,647. Therein the flash economizer was located between the condenser and the evaporator and the flashed gaseous refrigerant therefrom was drawn into the compressor between the first and second stages and the liquid refrigerant which has been cooled in the flashing process is allowed to travel to the evaporator.
Other types of multi-stage compressors have been used with various economizers. In Weller, et al, U.S. Pat. No. 3,232,074, entitled "Cooling Means for Dynamo Electric Machine" there is disclosed an evaporator and a condenser wherein the flash economizer is located therebetween, the flashed gas being drawn into the second stage of a two-stage compressor and liquid refrigerant passing through the condenser and to the machine for cooling of the electric motor. Other economizers are shown in Ware, U.S. Pat. No. 3,165,905; in Osborne, U.S. Pat. No. 3,553,974; in Hieatt, et al, U.S. Pat. No. 2,648,579; and in Anderson, et al, U.S. Pat. No. 3,665,724.
In Jeket, U.S. Pat. No. 3,226,940 an economizer is used with a centrifugal compressor having a combination impeller blade such that the flash gas from the economizer may enter the centrifugal compressor in the middle of the blade thereby creating within a single compressor two separate pressure levels. In Grandryd, U.S. Pat. No. 4,014,182, apparatus is disclosed wherein an economizer is utilized within a single stage compressor such that liquid refrigerant is allowed to flow from the condenser to the economizer wherein gaseous refrigerant is withdrawn into the compressor until such time as the economizer temperature reaches the desired level. At such time a valve opens allowing the refrigerant to be drawn into the chiller from which the compressor removes the flashed refrigerant gas. The compressor runs continuously however the suction line to the compressor is cycled alternately between the economizer and the condenser such that the compressor is steadily drawing refrigerant from either the economizer or the condenser and such that the refrigerant passing from the economizer to the condenser is always at the desired temperature.
A separate method is disclosed herein for removing the flashed refrigerant gas from a flash economizer. This method includes using an economizer-condenser for condensing the gaseous refrigerant to a liquid thereby reducing the pressure within the flash economizer such that additional liquid refrigerant entering the flash economizer may be flashed to absorb heat from the remaining liquid refrigerant. This thermal economized flash economizer system is particularly adaptable to a retrofit market for use with a refrigeration machine having a multi-stage compressor. Furthermore a valve may be located between the compressor and the flash economizer to control the amount of flashed gas drawn from the flash economizer to the compressor. The amount of flashed gas drawn into the compressor as controlled by the valve is dependent on the capability of the economizer condenser to recondense the flashed gas. The valve itself is controlled through a device which senses the temperature differential between the entering cooling fluid for the economizer-condenser and the liquid refrigerant within the flash economizer.
It is necessary to use flash type sub-cooling for certain selected refrigerants. Refrigerants such as R-11 are not readily adaptable to sensible heat sub-cooling and consequently the only satisfactory method of cooling R-11 is by latent heat cooling with a change in state from a liquid to a gas.
For a better explanation of the use of an economizer-condenser with a flash economizer refrigeration system see patent applications entitled "Dual Flash Economizer Refrigeration System", Ser. No. 828,458; "Dual Flash and Thermal Economized Refrigeration System", Ser. No. 828,793; and "Thermal Economized Refrigeration System", Ser. No. 828,449; all filed simultaneously herewith and all assigned to the assignee hereof.